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Archibald Scott Couper in 1858 and Johann Josef Loschmidt in 1861 [37] suggested possible structures that contained multiple double bonds or multiple rings, but in these years very little was known about aromatic chemistry, and so chemists were unable to adduce appropriate evidence to favor any particular formula.
Comparing the two contributing structures of benzene, all single and double bonds are interchanged. Bond lengths can be measured, for example using X-ray diffraction. The average length of a C–C single bond is 154 pm; that of a C=C double bond is 133 pm. In localized cyclohexatriene, the carbon–carbon bonds should be alternating 154 and 133 pm.
According to the rules expressed above, the phenanthrene molecule allows two different resonance structures: one of them presents a single circle in the center of the molecule, with each of the two adjacent rings having two double bonds; the other one has the two peripheral rings each with one circle, and the central ring with one double bond.
Expressing resonance when drawing Lewis structures may be done either by drawing each of the possible resonance forms and placing double-headed arrows between them or by using dashed lines to represent the partial bonds (although the latter is a good representation of the resonance hybrid which is not, formally speaking, a Lewis structure).
[18] [19] The LDQ structure for benzene is shown below. [16] [24] The LDQ structure of benzene. The carbon nuclei are coloured brown and the hydrogen nuclei are coloured pink, while the electrons are coloured either purple or green to distinguish between the spin sets. Left: The dot-and-cross diagram of the LDQ structure of benzene.
The phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen, which may be replaced by some other element or compound to serve as a functional group. A phenyl group has six carbon atoms bonded together in a hexagonal planar ring, five of which are bonded to individual hydrogen atoms, with the remaining ...
Line bond structure of benzene [5] Electron flow through p orbitals showing the aromatic nature of benzene [5] Benzene, C 6 H 6, is the least complex aromatic hydrocarbon, and it was the first one defined as such. [6] Its bonding nature was first recognized independently by Joseph Loschmidt and August Kekulé in the 19th century. [6]
The term itself is a general representation of electron density or configuration resembling a similar "bent" structure within small ring molecules, such as cyclopropane (C 3 H 6) or as a representation of double or triple bonds within a compound that is an alternative to the sigma and pi bond model.